Optical communication systems are known in which optical signals carrying data are transmitted from a first node to a second or receive node over an optical fiber. At the receive node, the optical signals are converted into corresponding electrical signals, which are then further processed.
The optical signals may be subject to chromatic dispersion (CD) in which various frequency components in each signal travel at different velocities. As a result, the in-phase (I) and quadrature (Q) components of electronic signals representative of data carried by the optical signals may have different delay and frequency response characteristics. Such differences may be resolved and CD compensation can be achieved electronically, in part, by converting the electronic signals into the frequency domain and conjugating the resulting frequency domain data in accordance with a Hermetian operation.
FIG. 1 illustrates a conventional circuit 301 that performs electronic CD compensation. Circuit 301 includes FFT block 302, which receives the electronic signals representative of data carried by the optical signal and outputs frequency domain signals. The frequency domain signals are then filtered in block 310, which includes Hermetian transpose circuit 304, N-tap FIR filter 306, and N-tap FIR filter 308. Namely, each output from FFT block 302 is supplied to a corresponding input or tap of filter 306 and multiplied by a corresponding coefficient. The resulting products are then summed to yield a first output. Each output of FFT block 302 is also conjugated by Hermetian transpose circuit 304, and each of the conjugated outputs is supplied to a corresponding input or tap of N-tap FIR filter 308 and multiplied by a corresponding one of the coefficients to yield a second output. The resulting products generated in N-tap FIR filter 308 are summed to yield a second output. The first and second outputs of filters 306 and 308 are then added by adder 312.
The coefficients of N-tap FIR filters 306 and 308 are chosen such that the resulting sum output from adder 312 is representative of CD compensated data in the frequency domain. The differences between the delay and frequency response of the I and Q components associated with such CD compensated data are eliminated or reduced. The output from adder 312 is next supplied to IFFT 314, which converts such data into the time domain.
As data or baud rates increase, the number of bits supplied to circuit 301 also increases. In order to process additional data, FFT 302, FIR filters 306 and 308, as well as IFFT 314 may be provided with additional inputs (e.g., taps) and outputs, as well as additional components (e.g., transistors or gates). These circuits may also be rendered more complex and may be required to consume additional power. An apparatus, method, and system are thus needed for more efficient realization of CD compensation circuitry that operates at higher data rates.